The United States imports an estimated 7 million tons of cargo transported by air with the annual amount of air freight continually growing. Air transportation constitutes the highest value cargo of any method of transportation, and its disruption, such as through terrorist attacks, would have very negative effects on the global economy. One potential risk is that terrorists may exploit air-cargo vulnerabilities to introduce an explosive device in cargo transported aboard a passenger aircraft or smuggle a weapon of mass destruction (WMD) within cargo transported on either passenger or cargo aircraft. Therefore, it has been mandated that all cargo transported on passenger aircraft be screened for explosives. In addition, there is a need to detect contraband, narcotics, currency, chemical and nuclear weapons, or any other material that could be of interest and that may also undergo cargo-manifest verification.
Detection of contraband with both high detection rates and low false alarm rates is a daunting task, as illegal, banned, or otherwise regulated materials often have similar physical characteristics as benign cargo. The percentage of cargo to be inspected is increasing and, because of the currently manually intensive nature of inspections, so must the number of operators. Therefore, there is a need to provide an automatic detection system to reduce the number of operators, or at least provide assistance tools that help operators improve their throughput by scrutinizing the cargo images more efficiently, thereby increasing detection and analysis speed.
Current explosives detection systems used in air-cargo facilities include, but are not limited to, break-bulk and X-ray pallet scanners, Explosives Trace Detectors (ETDs), canine inspection, and manual inspection. These methods suffer from one or more deficiencies such as low detection performance, low throughput to meet peak demand, and large staffing demands. While EDSs used for inspecting checked luggage provide high explosive detection performance, they have a small tunnel size suitable only for break-bulk cargo, requiring unpacking and reassembly of larger pallets, which results in slow throughput and larger staffing. In addition, these systems are expensive and are not easily afforded by private screeners. ETDs are slow, and the detection probability depends on the explosives packing method and the system sampling method. Canine inspection has the disadvantages of the significant effort of maintaining a canine operation and the cost of ownership. Manual inspection is time consuming and has low detection performance. Thus, there is a need for cost-effective inspection systems with improved detection to scan large objects.
Both standard and advanced X-ray scanner systems have difficulty detecting contraband in break-bulk cargo. This difficulty is exacerbated when inspecting larger and/or cluttered pallets and cargo containers. Large cargo containers require a relatively higher energy to be efficiently and effectively scanned for items of interest. There are some systems that produce high-resolution, dual-energy images and penetrate the majority of containers. However, these systems take approximately one hour to scan a container, thus requiring a large infrastructure which tends to be expensive for wide deployment. Therefore, at the higher energy required these approaches are not suitable for implementation due to cost, size, and complexity.
Further, while Computed Tomography (CT)-based systems have been shown to be more suitable for the difficult task of detecting aviation-threat explosives in luggage and, more recently, in larger objects, existing high-energy CT systems for large objects are configured horizontally (horizontal gantry) with the object rotating about its axis. In one case, the source and detectors move vertically, and in the other case, the object moves vertically while the source and detectors are stationary. In both cases, the length of the scanned objects is limited by the system size and the configuration prevents scaling the system up to long objects such as large cargo containers and large skids.
A trade-off between CT and dual-view radiography is a multi-view system, illustrated in FIG. 1, for example. The traditional approach is based on a few commercial X-ray sources 102 (for example, 2-3 sources) coupled with a few detector arrays 104 (for example, 2-5 detector arrays) to produce multiple views of an object 106 being scanned as it is conveyed through the system.
Another system based on these principles has been scaled up to scan palletized cargo. Additional views are obtained employing a rotating stage with a similar concept to that shown in FIG. 1. In this approach, the cargo is rotated by the desired angle (for example, 45°) and rescanned to generate additional views to improve the quality of the 3D images. The rotating stage reduces the need for additional sources and detectors. The disadvantages include lower throughput as the number of views increases, high cost, large footprints, and low performance since the number of views is typically too few for an acceptably enhanced 3D image quality that is sufficient for high detection performance.
Therefore, there is a need for detection systems which are cost-effective, have a high throughput, and are sufficiently compact to allow improved detection while scanning large objects such as cargo positioned on skids.